This invention relates to a hot top for ingot molds. It relates particularly to a superimposed hot top designed to rest on top of an ingot mold.
The typical superimposed hot top is comprised of an iron or steel casting lined with replaceable refractory material and provided with a tapering upwardly central opening or cavity. Molten metal is poured through such opening into the ingot mold positioned underneath the hot top. Pouring of the molten metal is continued until the level of the molten metal rises to a predetermined height in the hot top cavity to form a reservoir of molten metal that will feed metal downwardly into the ingot to overcome shrinkage during the solidification of the ingot.
The hot top must be designed not only to provide a sufficient reservoir of molten metal to fill the shrinkage cavity in the ingot, but also must reduce the heat losses from such reservoir to insure that the molten metal in the hot top reservoir remains molten during the solidification of the ingot.
After the ingot has solidified, the hot top casing is removed and the ingot is stripped from the ingot mold. The solidified metal that remained in the hot top, called the "sinkhead" is then cropped from the ingot and scrapped after the ingot is rolled. The scrapped sinkhead is thus unusable metal and with many ingots can amount to as much as 13-15 percent of the ingot volume.
In the past, there have been many attempts to reduce the size of the sinkhead to be scrapped by specially designed ingot molds and hot tops. However, such attempts have frequently resulted in ingots of poor quality, problems in rolling the ingots, or been restricted to relatively small size ingots.
One such specially designed hot top is that disclosed in U.S. Pat. No. 2,846,741, issued in 1958 to Whitacre. Whitacre designed the hot top cavity in the form of a substantially circular hollow cylinder to reduce the volume of molten metal in the hot top reservoir and to reduce heat losses. Whitacre suggests that the scrapped sinkhead will amount to 10 percent or less of the volume of the ingot. However, Whitacre's hot top design will likely produce problems during the stripping and the rolling of the ingot.
U.S. Pat. No. 1,207,645, issued in 1916 to Slick, and U.S. Pat. No. 3,437,308, issued in 1969 to Thiem et al, each show attempts to use an eight sided hot top cavity to reduce the reservoir volume and heat losses during solidification. To date, there has been no usage of such hot tops in the steel industry except for very small ingots.